Drop-dead heat ahead – report
CLIMATE CHANGE: KILLER HEATWAVES ON HORIZON
Updated projections indicate it may not be another century away.
Searing, unrelenting heat scorches large swathes of the earth, killing millions who have no means to escape. Shade is useless, and shallow bodies of water are warmer than the blood coursing through people’s veins.
This is a scene from a new sci-fi novel, but the suffocating horror it describes may be closer to science than fiction, according to a draft UN report that warns of dire consequences for billions if global warming continues unchecked.
Earlier climate models suggested it would take nearly another century of unabated carbon pollution to spawn heatwaves exceeding the absolute limit of human tolerance. But updated projections warn of unprecedented killer heatwaves on the near horizon, according to a Intergovernmental Panel on Climate Change (IPCC) report, scheduled for release in February next year.
The chilling report paints a grim – and deadly – picture for a warming planet. If the world warms by 1.5ºC – 0.4ºC above today’s level – 14% of the population will be exposed to severe heatwaves at least once every five years, “a significant increase in heatwave magnitude”, the report says.
Going up half a degree would add another 1.7 billion people.
Worst hit will be burgeoning megacities in the developing world that generate additional heat of their own, from Karachi to Kinshasa, Manila to Mumbai, Lagos to Manaus.
It’s not just thermometer readings that make a difference – heat becomes more deadly when combined with high humidity.
It is easier, in other words, to survive a high temperature day if the air is bone-dry than to survive a lower temperature day with very high humidity.
That steam-bath mix has its own yardstick, known as wetbulb temperature.
Experts say healthy human adults cannot survive if wet-bulb temperatures (TW) exceed 35ºC. “When wet-bulb temperatures are extremely high, there is so much moisture in the air that sweating becomes ineffective at removing the body’s excess heat,” said Colin Raymond, lead author of a recent study on heatwaves in the Gulf.
“Perhaps after six or more hours, this will lead to organ failure and death in the absence of access to artificial cooling.”
Heat stroke, heart a acks
We’ve already seen the impact of deadly, humid heat at far lower thresholds, especially among the elderly and infirm. Two heatwaves in India and Pakistan that hit 30ºC TW in 2015 left more than 4 000 people dead.
And the 2003 heatwave that killed more than 50 000 people in western Europe registered wetbulb temperatures only in the high 20s.
Blistering heatwaves across the northern hemisphere in 2019 – the second warmest year on record for the planet – also caused a large number of excess deaths, but wet-bulb data is still lacking.
Research from the Institute for Health Metrics and Evaluation reports just over 300 000 heat-related deaths worldwide in 2019.
Some 37% of heat-related deaths – just over 100 000 – can be blamed on global warming, according to researchers at the London School of Hygiene & Tropical Medicine. In half-a-dozen countries – Brazil, Peru, Colombia, the Philippines, Kuwait and Guatemala – the percentage was 60% or more. Most of these deaths were probably caused by heat stroke, heart attacks and dehydration.
Cities at risk
Dangerous spikes above 27ºC TW have already more than doubled since 1979, according to Raymond’s findings. His study predicts wet-bulb temperatures will “regularly exceed” 35ºC TW at some locations in the next several decades if the planet warms 2.5ºC above preindustrial levels.
Human activity has driven global temperatures up 1.1ºC so far. The 2015 Paris Agreement calls for capping the increase at “well below” 2ºC, and 1.5ºC if possible. Even if those targets are met, hundreds of millions of city dwellers in sub-Saharan Africa, as well as South and Southeast Asia, will likely be afflicted by at least 30 deadly heat days every year by 2080, the IPCC report says.
“In these regions, the population of cities is growing dramatically and the threat of deadly heat is looming,” said Steffen Lohrey, lead author of a study, still under peer review, cited in the report.
His calculations, Lohrey added, do not even take into account the so-called urban heat island effect, which adds 1.5ºC on average during heatwaves.
Heatwave ‘hotspot’
Sub-Saharan Africa is especially vulnerable to lethal heatwaves, in large part because it is least prepared to cope with them.
“Real-world observations and climate modelling show sub-Saharan Africa as a hotspot for heatwave activity,” said Luke Harrington, a postdoctoral researcher at the University of Oxford’s Environmental Change Institute.
In central China and central Asia, “extreme wet-bulb temperatures are expected to approach and possibly exceed physiological thresholds for human adaptability”, the IPCC warns.
The Mediterranean is also vulnerable. “In Europe, up to 200 million people will be at high risk of heat stress by mid-century if the world warms up to 2ºC until 2100,” the report says.
Cooling gap
But the effects of heatwaves are not felt evenly. In some developing countries, economic development is not keeping up with the cost of cooling the population.
But ultimately, high heat will destroy more lives indirectly, the IPCC report suggests. Higher temperatures will spread disease vectors, reduce crop yields and nutrient values, slash labour productivity and make outdoor manual labour a life-threatening activity.